This appears to be in the same series as a 1921 booklet about California and a 1923 booklet about the Pacific Northwest. However, the PNW booklet is a different size (8×9 vs. 6×9) and has flimsy (but glossy) covers, while the California and Colorado booklets have stiffer (but not glossy) covers. The cover paintings are similar and, though I can’t find an artist’s name on any of the covers, it is possible that the same artist did the Colorado and Northwest covers. Inside, the numerous photos are all black-and-white or, actually, blue-and-white.
Page 30 features a photo of Union Pacific locomotive 7000, a 4-8-2 Mountain-type, pulling a passenger train across the prairie, presumably towards Colorado. This locomotive, which the UP called a Sports Model, was built in 1922 and represented the newest and most-powerful passenger locomotives on the UP roster at that time. The Mountain type got its name from the Allegheny Mountains, as it was pioneered by the Chesapeake and Ohio eleven years before UP bought the 7000, its first 4-8-2.